The present invention relates to etching an etch layer through a mask during the production of a semiconductor device. More specifically, the present invention relates to CD bias loading control for fine features with opening of an antireflective coating (ARC) layer through a mask during an etching process for the production of semiconductor devices.
During semiconductor wafer processing, features of the semiconductor device are defined in the wafer using well-known patterning and etching processes. In these processes (photolithography), a photoresist (PR) material is deposited on the wafer and then is exposed to light filtered by a reticle. The reticle is generally a glass plate that is patterned with exemplary feature geometries that block light from propagating through the reticle.
After passing through the reticle, the light contacts the surface of the photoresist material. The light changes the chemical composition of the photoresist material such that a developer can remove a portion of the photoresist material. In the case of positive photoresist materials, the exposed regions are removed, and in the case of negative photoresist materials, the unexposed regions are removed. Thereafter, the wafer is etched to remove the underlying material from the areas that are no longer protected by the photoresist material, and thereby define the desired features in the wafer.
Typically, in photolithography steps, one or more antireflective coating (ARC) layers, for example, a bottom antireflective coating (BARC) and/or a dielectric antireflective coating (DARC) layer are provided under a photoresist mask. These layers minimize or eliminate reflections during exposure of the photoresist which may produce standing waves. Such standing waves may result in defects such as sinusoidal “scalloping” of the photoresist sidewalls, or the formation of “feet” at the base of the photoresist layer. Therefore, BARC/DARC layers are generally disposed below a photoresist layer and above other device materials (e.g. SiO2) to be etched through the photoresist mask. BARC/DARC layers may be organic-based or inorganic-based, and are usually composed of different materials than the underlying dielectric material. The BARC layer is usually organic, but an inorganic BARC layer may be composed of titanium nitride (TiN) as well as silicon oxynitride (SiON). The DARC layer may be formed of SiOx.
The critical dimension (CD) uniformity in ultra large scale integrated circuits (ULSI) is a crucial parameter for high performance devices. The CD uniformity in the gate electrode, for example, affects the threshold voltage distribution and the overall yield of the devices. The required CD of the features of a semiconductor device can be met by either controlling the CD of the photolithography or controlling the CD bias during the etch process. The CD bias (also referred to as CD skew) is the difference between a mask CD (before etching) and the CD of the resulting features (after etching). The CD bias accompanied by an etch process depends on the pattern density of the etch features, and generally, such CD bias is greater in an insolated-pattern area than that in a dense-pattern area. In general, the difference depending on a feature pattern is referred to as “loading.” The difference in an etch rate depending on the pattern is referred to as “etch-rate loading.” The difference in the CD bias depending on the pattern density is referred to as the CD bias loading (“Iso-Dense CD bias loading”). For example, FIGS. 1A and 1B schematically illustrate a patterned mask 10 and an etch layer 12 in a dense area 14 and an isolated area 16, respectively, before an etch process. FIGS. 2A and 2B schematically illustrate the etch layer 12 in the dense area 14 and the isolated area 16, respectively, after the conventional etch process. As shown in the figures, the CD bias, which is the difference between the mask CD1 and the etched feature CD2, is greater in the isolated area (FIG. 2B) than in the dense area (FIG. 2A). In addition, in general, it is more difficult to define a pattern of small CD in the isolated area (for example, a fine line pattern) than the dense area by photolithography. Thus, a greater CD bias loading makes it more challenging to define a small CD in the isolated-pattern area.